PDC cutters with improved toughness

ABSTRACT

A polycrystalline diamond layer attached to a cemented metal carbide structure used as a cutter wherein the cutter has improved toughness or fracture resistance during use through the inclusion of boron, beryllium or the like therein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polycrystalline diamond compositecompact for use in drilling operations which require high wearresistance of a diamond surface. More specifically, the presentinvention relates to a polycrystalline diamond layer attached to acemented metal carbide structure used as a cutter in a drill bit fordrilling operations wherein the cutter has improved toughness orfracture resistance, during use.

2. State of the Art

Polycrystalline diamond tools suitable for use in rock drillingoperations are well known. Typically, the polycrystalline diamondcutters used on such tools are composite compacts comprising apolycrystalline diamond layer and a cemented carbide support structure.Typically, the carbide support structure comprises tungsten carbidecontaining cobalt metal as the cementing constituent. The cobaltcontained in the carbide support structure functions as the bondingmetal for the carbide, as a sintering aid for consolidating the diamondparticles into a solid attached diamond layer, and to bond the diamondlayer to the carbide support. Care must be exercised regarding theamount of cobalt used as an excessive amount of cobalt infiltrated fromthe carbide support structure into the diamond layer leaves an excessiveamount of cobalt among the diamond particles thereby affecting themechanical properties, possibly causing less than optimal abrasionresistance of the diamond layer. Also, the physical and mechanicalproperties of the cemented carbide support structure near thediamond/carbide interface are affected as a result of the cobaltdepletion from the carbide support. Typically, the cobalt depletion ofthe carbide support structure adjacent to the interface results inreduced mechanical properties in a critical area of the diamond tungstencarbide cutter.

Various methods are used to control the cobalt infiltration into thediamond to prevent excessive infiltration into such layer and theattendant cobalt depletion of the carbide support structure. Typicallyprior art diamond cutters are described in U.S. Pat. Nos. 4,988,421;5,011,514; 5,011,515; 5,022,894; 5,111,895; 5,151,107; and 5,176,720 aswell as European Patent Application 0,246,789.

Also, attempts have been made to increase the hardness of cementedcarbide bodies, which bodies include a tungsten backing of thepolycrystalline diamond compact, are made by sintering pressed carbidepowders to provide cutting implements having the ability to hold asharper edge or longer life. Such cemented carbide bodies typically arecomprised of a mixture of tungsten carbide and cobalt. Typically, informing such bodies a trade-off occurs between brittleness and hardness.The harder the body is the better the body holds a cutting edge;however, the more brittle the body.

One attempt to avoid the increased brittleness while improving hardnesshas been to produce a thin surface coating or layer on the carbide bodycontaining boron by diffusing boron into the surface of the cementedcarbide body. However, as the thin coating is worn away the improvedproperties of hardness as well as other features are lost. Anotherattempt has been made to improve the properties of a cemented carbidebody made by sintering pressed carbide powders in the presence of boroncontaining material to diffuse the boron to a greater depth in thecemented carbide body. Such cemented carbide bodies are described inU.S. Pat. Nos. 4,961,780 and 5,116,416. These types of cemented carbidebodies including boron show improved fracture toughness over bodieswhich contain no boron.

SUMMARY OF THE INVENTION

The present invention relates to a polycrystalline diamond layerattached to a cemented metal carbide support structure used as a cutterin a drill bit for drilling operations wherein the cutter has improvedtoughness or fracture resistance during use. The present invention isdirected to a cutter comprising a polycrystalline diamond layer and acemented support structure including tungsten carbide, boron and cobalt.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a free-standing typical cutting element of thepresent invention.

FIG. 2 illustrates the cutting element of the present invention in aportion of a drill bit.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

The present invention provides a method for making backed abrasivecompacts having an improved toughness or fracture resistance during use.Referring to drawing FIG. 1, a composite compact 10 comprising acemented carbide support structure 12 and a polycrystalline diamondtable or layer 14 is shown.

The composite compacts for use in rock drilling and machining are wellknown in the art, such as described in U.S. Pat. No. Re. 32,380. Asdescribed, the composed compact comprise a polycrystalline diamond layerwherein the diamond layer is bonded by the use of cobalt to the cementedcarbide support material which is considerably larger in volume thanthat of the volume of the polycrystalline diamond layer. Typically, thecarbide support structure is tungsten carbide containing cobalt metal asthe cementing constituent.

As previously stated, the cobalt contained in the carbide supportstructure makes itself available to function both as the metal bond forsintering the tungsten carbide, a diamond sintering aid to facilitatesintering of the diamond powder, and to bond the sintered diamond layerto the carbide support.

While it is possible to limit or control the cobalt depletion from thecarbide support through a variety of manners, some cobalt typicallyinfiltrates into the polycrystalline diamond layer of the compositecompact leaving a depleted zone in the adjacent carbide support. Thedepleted zone 16 is shown in the carbide support 12 in drawing FIG. 1.

As a result of the cobalt being present in the interstices between thediamond particles, the diamond layer 14 degrades at a lower temperature.Also, a small region between the diamond layer 14 and the bulk of thecarbide support 12 has reduced mechanical properties, such as fracturetoughness, as cobalt has been depleted from the zone 16 of the carbidesupport 12. This makes the zone 16 more susceptible to crack formationand propagation.

The present invention utilizes boron to control the fracture toughnessproperties of the zone 16 from which cobalt is depleted during thediamond layer sintering. The polycrystalline diamond compact hasimproved toughness or fracture resistance as a result of the inclusionof boron in the zone 16 of the support 12.

The improved toughness or fracture resistance of the compact issignificantly improved in those compacts using lower percentages ofcobalt in the carbide support structure. The cobalt content of thedepleted zone 16 is such that a relatively large improvement oftoughness occurs.

One manner of controlling the fracture toughness in the zone 16 is tomix or include boron with the material used to form the supportstructure 12 prior to the sintering.

Another manner of controlling the fracture toughness in the zone 16 isto provide a boron containing gas in the atmosphere surrounding thecarbide support structure 12 during the sintering of the supportstructure 12.

As a result of controlling the amount of cobalt swept into the diamondlayer from the carbide support structure with boron being at least inthe depleted zone 16, in low cobalt alloy carbide support structures thefracture toughness or fracture resistance is particularly improved.

As previously stated, the use of boron in the area for the interface ofthe diamond layer 14 and carbide support structure 12 of compacts 10appears to be most effective in improving the fracture toughness orfracture resistance in compacts where the carbide support structure 12typically contains twelve percent to twenty percent (12%-20%) cobalt inthe depleted zone 16 before any cobalt depletion has occurred. Thisyields a cobalt percentage of three percent to thirteen percent (3%-13%)after depletion.

In the present invention, it is preferred that the carbide substrate orsupport structure 12 include boron in approximately a concentrationrange of 200 to 700 parts per million (ppm). The present inventionimproves the fracture toughness in the zone 16 of the support structure12 to help prevent cracking in the zone 16 and any crack propagationfrom the zone 16 either into the diamond layer 14 or support structure12 of the compact 10.

While the present invention has been described with respect to the useof boron in the support structure 12, other materials may be used togive improved fracture toughness, such as beryllium and the like.Referring to drawing FIG. 2, the compact 10 of the present invention isshown mounted on a portion of a drill bit 1 shown in broken lines.

It will be understood by those of ordinary skill in the art thatchanges, modifications, deletions, and additions may be made which fallwithin the scope of the invention.

What is claimed is:
 1. A polycrystalline compact comprising:a carbidesubstrate comprising a member having a first end, first end regionlocated adjacent the first end, a second end, and remaining region, thecarbide substrate having cobalt non-uniformly dispersed thereinthroughout the first end region and the remaining region thereof, thefirst end region located adjacent the first end of the carbide substratehaving less cobalt therein than the remaining region of the carbidesubstrate; a polycrystalline material layer joined to the carbidesubstrate the polycrystalline material joined to the first end of thecarbide substrate; and a quantity of boron located in the first endregion located adjacent the first end of the carbide substrate joined tothe polycrystalline substrate material layer thereby resulting inimproved fracture toughness of said polycrystalline compact.
 2. Thepolycrystalline compact of claim 1, wherein the carbide substratecontains a quantity of boron therein.
 3. The polycrystalline compact ofclaim 1, wherein the polycrystalline layer comprises diamond.
 4. Thepolycrystalline compact of claim 1, wherein the carbide substratecomprises tungsten carbide.
 5. The polycrystalline compact of claim 4,wherein the carbide substrate further comprises tungsten carbide andcobalt.
 6. The polycrystalline compact of claim 1, wherein the carbidesubstrate comprises less than seven percent cobalt.
 7. Thepolycrystalline compact of claim 1, wherein the carbide substratecomprises less than ten percent cobalt.
 8. The polycrystalline compactof claim 1, wherein the carbide substrate comprises less than twentypercent cobalt.
 9. The polycrystalline compact of claim 1, wherein thecarbide substrate comprises less than thirty percent cobalt.
 10. Thepolycrystalline compact of claim 1, wherein the carbide substratecomprises approximately 200-700 ppm of boron.
 11. A polycrystallinecompact comprising:a carbide substrate having cobalt therein; apolycrystalline material layer joined to the carbide substrate; and aquantity of beryllium used in the carbide substrate during the formationthereof thereby resulting in improved fracture toughness of saidpolycrystalline compact.
 12. A polycrystalline compact comprising:acarbide substrate comprising a member having a first end, first endregion located adjacent the first end, a second end, and remainingregion, the carbide substrate having cobalt non-uniformly dispersedtherein throughout the first end region and the remaining regionthereof, the remaining region of the carbide substrate having morecobalt therein than the first end region of the carbide substrate; apolycrystalline material layer joined to the carbide substrate, thepolycrystalline material joined to the first end of the carbidesubstrate; and a quantity of boron located in the first end regionlocated adjacent the first end of the carbide substrate joined to thepolycrystalline substrate material layer thereby resulting in improvedfracture toughness of said polycrystalline compact.
 13. Apolycrystalline compact comprising:a carbide substrate comprising amember having a first end, first end region, second end, and remainingregion, the carbide substrate having cobalt non-uniformly dispersedtherein throughout the first end region and the remaining regionthereof, the first end region located adjacent the first end of thecarbide substrate having less cobalt therein than the remaining regionof the carbide substrate; a polycrystalline material layer joined to thecarbide substrate, the polycrystalline material joined to the first endof the carbide substrate; and a quantity of beryllium located in thefirst end region located adjacent the first end of the carbide substratejoined to the polycrystalline substrate material layer thereby resultingin improved fracture toughness of said polycrystalline compact.